The male attacker carried out attacks on passersby, causing stab wounds to eight while moving along central streets of the city at about 11.20am local time, said Russia’s Investigative Committee, which investigates major crimes.

“The committee is investigating attempted murder,” a spokeswoman told Reuters. She would not comment on whether the incident was terrorism related.

Surgut is 2,100km (1,330 miles) north-east of Moscow in the oil-rich Khanty-Mansi region.

Four of the wounded were in serious condition, according to Tass , which cited regional health official Vladislav Nigmatulin. The government of the Khanty-Mansi region said the attacker remained unidentified.

The government called for calm over the incident, urging “citizens and media … to use reliable information in assessing the situation until all the circumstances are established”.